This proposal describes three avenues of investigation to be conducted on insect ion transport epithelia: 1) In the lower Malpighian tubule of Rhodnius prolixus the mitochondria migrate upon hormone stimulation from the interior of the cytoplasm to a position adjacent to the transport membrane, the luminal microvilli. The role of microfilaments and microtubules in this movement will be investigated. The mechanism of hormone stimulation of the movement via secondary messengers such as calcium or cyclic AMP, and the influence of mitochondrial movement and location on rates of ion transport will be determined. 2) Septate and continuous junctions in epithelia which are known to have different water permeabilities will be compared using lanthanum and microperoxidase as extracellular markers, freeze fracture to examine the intramembrane morphology of the junctions and shadow-cast replicas to examine extracellular componenets. This information will be related to the osmotic permeability of the junctions. 3) The role of gap junctions in the spread of hormone activation will be examined. Isolated regions of Malpighian tubule, in vitro, can be stimulated and response measured at discrete locations along the tubule. Gap junction uncouplers (calcium, laser microinjury etc.) will be used to stop the spread and demonstrate gap junction involvement.